1. Field of Invention
The present invention is related to flexible circuit board, and more specifically, to a flexible circuit board having a specific structure to alleviate mechanical stress thereof.
2. Description of Related Art
With the development of packaging technology, chip on film (COF) bonding technology has become one of the progressive packaging technologies. Generally, COF bonding technology can be applied broadly, for example, the electrical connection between a liquid crystal panel and a driver IC is one of the applications using COF bonding technology.
Referring to FIGS. 1 and 2. FIG. 1 is a cross-sectional diagram of an electronic apparatus 4, and FIG. 2 is a cross-sectional diagram of another electronic apparatus 6. Each of the electronic apparatuses 4 and 6 could be, for example, a thin film transistor liquid crystal display (TFT-LCD), a plasma display, an organic light-emitting diode display (OLED), etc. Each of the electronic apparatuses 4 and 6 has a display panel 8, a printed circuit board (PCB) 10, a driver IC 12, and a flexible circuit board 14. The PCB 10 has an embedded timing controller for generating a timing signal to control the operations of the driver IC 12. The flexible circuit board 14 could be bent such that the PCB 10 could be positioned on the top of the electronic apparatus 4 (as shown in FIG. 1) or positioned behind the display panel 8 (as shown in FIG. 2). The driver IC 12 is formed on the flexible circuit board 14 and operates according to the timing signal received from the timing controller embedded in the PCB 10.
Referring to FIG. 3, which is a schematic diagram of the display panel 8, the PCB 10, the driver IC 12, and the flexible circuit board 14. The driver IC 12 formed on the flexible circuit board 14 is electrically connected to the PCB 10 via a plurality of wires 16 and to the display panel 8 via a plurality of wires 18. Each of the wire 16 has an outer lead 1a, an inner lead 1b, and a connection portion 1c that connects to the outer lead 1a with the inner lead 1b. As shown in FIG. 3, the width of the outer leads 1a is greater than the width of the inner leads 1b, and the wires 16 are warped and have sharp corners. However, since the flexible circuit board 14 is bent, the joint portion of the outer lead 1a and the connection portion 1c and the joint portion of the inner lead 1b and the connection portion 1c are easily to be broken due to their high stress concentrations resulted from the sharp corners, such that the signal transmission between the PCB 10 and the driver IC 12 would be failed.
In a Japan published patent application NO. H11/345839, a flexible circuit board is disclosed. Referring to FIGS. 4 and 5. FIG. 4 is a schematic diagram of the flexible circuit board disclosed in the Japan published patent application, and FIG. 5 is an enlarged diagram of a wire of the flexible circuit board shown in FIG. 4. As shown in FIG. 4, two wires of the flexible circuit board are respectively formed with a corresponding indentation 2. Each of the indentations 2 is a rounded concave section of the interior side, which could alleviate the mechanical stress of an inner side 2a of the joint portion of the outer lead 1a and the connection portion 1c. However, the joint portion 2b of the inner lead 1b and the connection portion 1c is a sharp corner, thereby still suffering a high stress concentration that increases the possibility that the joint portion 2b may break under force.